Searching for objects is a fundamental problem for popular peer-to-peer
file-sharing networks that contribute to much of the traffic on today's
Internet. While existing protocols can effectively locate highly popular
files, studies show that they fail to locate a significant portion of
existing files in the network. High recall for these ``rare'' objects
would drastically improve the user experience, and make these networks
the ideal distribution infrastructure for user-generated content such as
home videos and photo albums. In this paper, we examine simple
techniques that can improve search recall for rare objects while
minimizing the overhead incurred by participating peers. We propose
several strategies for multi-hop index replication, and demonstrate
their effectiveness and efficiency through both analysis and simulation.
We further evaluate our simple techniques using detailed traces from a
real Gnutella network, and show that they improve the performance of
these overlays by orders of magnitude in both lookup success and
overhead.